Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH 15/19] mm: Kill off ACCESS_ONCE() | Date | Mon, 23 Oct 2017 14:07:25 -0700 |
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For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful.
However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation.
It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the mm code and comments to use {READ,WRITE}_ONCE() consistently.
---- virtual patch
@ depends on patch @ expression E1, E2; @@
- ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2)
@ depends on patch @ expression E; @@
- ACCESS_ONCE(E) + READ_ONCE(E) ----
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> --- mm/memory.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c index a728bed16c20..cae514e7dcfc 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3891,9 +3891,9 @@ static int handle_pte_fault(struct vm_fault *vmf) /* * some architectures can have larger ptes than wordsize, * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and - * CONFIG_32BIT=y, so READ_ONCE or ACCESS_ONCE cannot guarantee - * atomic accesses. The code below just needs a consistent - * view for the ifs and we later double check anyway with the + * CONFIG_32BIT=y, so READ_ONCE cannot guarantee atomic + * accesses. The code below just needs a consistent view + * for the ifs and we later double check anyway with the * ptl lock held. So here a barrier will do. */ barrier(); -- 2.5.2
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